They Came from Beneath the Sea was a documentary which examined the Silurians, the Sea Devils and the Myrka in the Doctor Who television story Warriors of the Deep. The documentary was included in the DVD release of Warriors of the Deep, which was a part of the Beneath the Surface box set.
Writer Johnny Byrne discussed the inclusion and development of the Silurians, the Sea Devils and the Myrka in the story, while actor Peter Davison talked about the Sea Devils' voices as opposed to the Silurians' voices. Director Pennant Roberts discussed the direction of the story and visual effects designer Matt Irvine talked about the new design of the Silurians and the Sea Devils. A main feature of the documentary was the discussion of the Myrka. Johnny Byrne mentioned that the creature was "an ineffectual creature in the history of Doctor Who". Matt Irvine talked about the creation and the design of the Myrka. Actors John Asquith and William Perrier, who played the Myrka, discussed how they played it and the limitations in doing so. They demonstrated how they played the Myrka.
The documentary used scenes from the episode below to highlight events mentioned by the interviewees.